Soft-Target Protection is a gear perk that reduces damage from soft-target rounds. It is the basic version of the soft-target defense perks and comes on the standard Soft-Target set.
Soft-target ammo hurts you less. It helps against enemies who use those rounds, but not against armored troops firing armor-piercing ammo.
Wear any piece of the Soft-Target set. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Fine early on. Swap to Soft-Target Defender later, since it also covers armor-piercing rounds.